Wheel speed detecting devices are mounted to vehicles such as motorcycles to detect the rotation speed of the wheels. Most wheel speed detecting devices used in vehicles are provided with a ring to be detected (also referred to as a detection target ring) such as a pulsar ring integrally and rotatably attached to a wheel of a wheel assembly and a rotation sensor such as a pickup sensor for detecting the rotation of the detection target ring.
A wheel speed detecting device used for a straddle-type vehicle such as a motorcycle is known in which a detection target ring is jointly fastened and fixed, together with a brake disc of a disc brake device, to a wheel of a wheel assembly, and a rotation sensor is attached to a vehicle body so as to face a detection target portion (for example, a pickup hole) of the detection target ring (see, for example, Patent Literature 1).
The detection target ring used in the wheel speed detecting device described in Patent Literature 1 includes an annular base wall having detection target portions and a plurality of ring attachment portions protruding radially outward from an outer peripheral edge portion of the base wall, wherein the outer peripheral edge portion of the base wall, which is adjacent to the ring attachment portions, is bent to improve the rigidity of the ring attachment portions. The detection target ring is disposed radially inward of the brake disc of the disc brake and the ring attachment portions protruding radially outward from the base wall are bolted, together with disc attachment portions of the brake disc, to the wheel of the wheel assembly.
In the brake device, when braking continues for a long time, much heat is generated between the brake disc and a friction material of a brake caliper and the heat thermally expands the brake disc or the wheel. In the wheel speed detecting device described in Patent Literature 1, the base wall of the detection target ring has bent portions and therefore, even when stress is applied to the ring attachment portions of the detection target ring due to thermal expansion and contraction of the brake disc or the wheel due to braking, the bent portions restrict deformation of the base wall due to the stress.